A colonoscopy is a very safe and effective investigation that lets your doctor examine the lining of your colon (large intestine).

In order to do the test your consultant will use a thin (thinner than your little finger), flexible tube called an endoscope. This has steering controls at one end and a digital camera and a bright light at the other. The detailed colour images of the colon and large intestine are displayed on a video monitor. The endoscope also allows the consultant to obtain tissue samples (biopsies), and remove polyps (benign growths in the lining of the bowel).

Your doctor will have recommended a colonoscopy. However, it is your decision whether to go ahead with the procedure or not. This information will explain the benefits and risks to help you make an informed decision.

A colonoscopy helps your doctor evaluate symptoms of diarrhoea, rectal bleeding, abdominal pain or anaemia, where there is the possibility of abnormalities in the lower bowel (large intestine or colon).

Benefits of having a colonoscopy

Colonoscopy allows the endoscopist to examine the colon, as far as the valve passing up into the small intestine (ileocaecal valve). The endoscopist is able to detect inflammation, ulceration, causes of bleeding, cancers, polyps and strictures (narrowing) in the colon. Through the colonoscope, tissue samples (biopsies) may be obtained, and other treatments carried out, such as removing polyps, cauterizing bleeding blood vessels, dilating (stretching open) areas of blockage. It is considered the most accurate technique of examining the colon, and the imaging technology of colonoscopy is improving all the time, with technical advances enabling easier detection of minor changes using magnification, dye spraying, and new optical techniques.

Colonoscopy is easily carried out on an outpatient basis using sedation and is very well tolerated by patients. The technique of endoscopy is extremely safe, with very low rates of complications, when performed by a properly trained consultant. A bowel clear-out with laxatives is required on the day before the colonoscopy.

A barium enema (X-ray test of the colon), provides images of the large intestine, but is less accurate at detecting small polyps, or subtle inflammation of the colonic lining. It does not enable tissue samples to be taken, or treatments to be carried out. It can be useful to rule out significant sized tumours or larger polyps. It still requires bowel clear-out with laxatives. CT colonography is another imaging technique, using CT scanning, after pumping air through the back passage to inflate the colon. Again, treatments or biopsies are not possible. If abnormalities are found, then a colonoscopy may have to be arranged.

Your doctor would discuss alternatives with you, as detailed above.

• Before the colonoscopy

Your colon needs to be empty before the test, so you need a clear-out with strong laxatives on the day before the test. This will result in diarrhea and this will continue for a few hours until the bowel is empty. In addition you will be instructed to drink plenty fluids, although these should only be clear fluids later on (nothing with milk in), and you will also be asked to restrict your diet prior to this.

If you are taking iron tablets or liquid, this should be stopped one week before the colonoscopy. Anti-diarrhoea drugs, such as loperamide, codeine, or lomotil should be stopped at least 24 hours before starting the bowel clear-out. Other drugs do not need to be stopped.

If you have diabetes, or are taking warfarin, or clopidogrel, you will be given advice beforehand.

On arrival in the endoscopy unit the staff will explain the procedure to you and the consultant will ask you to sign a consent form. This is to ensure that you understand the implications of the procedure and are happy to proceed. You will be asked to wear a gown.

• During the colonoscopy

A sedative and pain-killer is nearly always required for the test and a needle is placed in your hand or arm, prior to the procedure. A probe will be placed on a finger to monitor oxygen levels, and you will be given oxygen through a mask. The pain-killer (pethidine or fentanyl) and a sedative (midazolam) is given immediately before the colonoscopy. The sedative will make you drowsy and relaxed. Most patients don’t remember the first half of the procedure (while the scope is passed into the colon). The pain-killer is given, as there is sometimes griping discomfort as the scope passes around sharp bends in the colon. Most patients are awake for the second half of the procedure as the scope is withdrawn. This part is not painful, but sometimes there is a sensation of bloating and mild colicky discomfort afterwards, due to the air left behind in the bowel, which usually disappears over about an hour. The whole procedure usually takes about 20-30 minutes.

• After the procedure

Once the test is completed you will be transferred to the recovery area. You will need someone to bring you to the clinic and to drive you home. You should not drive for 24 hours after having  sedation, and should have someone with you at home until the following morning. Although you will be fully awake within one hour, the sedation takes a number of hours to completely wear off, and your memory and reaction times will not be completely normal. You may feel a bit bloated for a few hours after the colonoscopy, but this will pass. A member of the team will tell you what was found during the endoscopy and will discuss any treatment and follow up appointments you may need. You should be able to go back to work the day after the colonoscopy unless you are told otherwise. For further information, speak to your consultant or a member of the endoscopy team.

Colonoscopy is a very safe procedure, with a risk of significant complications of about 1 in 1,000 procedures. The experienced healthcare team will make every effort to minimize any risk associated with the procedure. However, there are potential complications of colonoscopy and these are listed below.

• Making a tear or perforation of the colon occurs in less than 1 per 1,000 procedures. It results in severe pain, and often requires surgery to correct. It is rarely fatal, but may require a stoma bag temporarily. The risk of perforation is related to treatments such as polyp removal, and many precautions are taken to minimize any risk.
• Bleeding from the bowel. This can be related to polyp removals or biopsies. Again, many safety procedures will minimize the risk, which is less than 1 in 500. Bleeding is usually self-limiting, and would occasionally require blood transfusion, and very rarely require corrective surgery.
• An adverse reaction to the sedation, as allergic reaction, respiratory suppression, or inflamed veins (phlebitis). This is very unusual and you will be adequately monitored until the sedation has worn off.

If you have any specific concerns about the procedure please raise these with the healthcare staff or consultant.